The purpose of the study is to determine the best course of action in the event chemical, biological or radiological materials are released in the city, whether intentionally or not. The research will help officials decide on evacuation or sheltering plans.

Police spokesman Paul Browne said the move wasn’t prompted by a specific threat in the city, but the nation’s biggest police department is taking no chances as it learns more about the attack on Kabul’s Inter-Continental Hotel, which is frequented by foreigners.